The invention relates to an apparatus for etching substrates with a luminous discharge in a vacuum, containing a vacuum chamber, a substrate holder, an electrode disposed opposite the substrate holder and substrates, and a radiofrequency generator with an output frequency above 100 kHz, preferably between 1 and 50 MHz, which is connected on the one hand to the substrate holder and on the other hand to the electrode. The electrode situated opposite the substrate holder and at least partially enclosed by a pot-shaped, grounded shield is provided in the marginal area with a projection which is at the same potential and spans the space between the electrode and the substrate holder except for a gap, such that the luminous discharge can be limited to the space between substrate and electrode.
It is known that a sputtering process can be performed by means of a high-frequency voltage between two electrodes if the electrode (target) consisting of the material to be sputtered is of smaller area than the counter-electrode. Then not only the substrate and the grounded substrate holder serve as the counter-electrode but also the likewise grounded chamber walls. As a result of these considerable differences in area, a substantially greater charge density occurs on the electrode being sputtered, and this is to be attributed to the different mobility of the charge carrier in the electrical field.
To limit the luminous discharge to the immediate area between cathode and anode, and consequently for the achievement of a high and uniform deposition rate, it has already been proposed in DE-OS No. 21 15 590 to provide the marginal zone of the cathode with a projection spanning the space between a discoidal part of the cathode and the substrate holder except for a gap, which in this case amounts to 5 mm. Due to the design of the power supply system, however, the apparatus in question is suitable only for coating the substrates, not for etching them. In the proposed system, at first the grounded electrode (substrate surface, substrate holder) was smaller than the area of the counter-electrode (target).
In the state of the art, different apparatus have had to be used for etching, on the one hand, and for coating, on the other. Yet even if two such systems were to be integrated in a single vacuum apparatus, if the separation of the electrical systems is to be complete, it would be necessary to provide additional insulation measures, shielding, and various impedance matching networks. This is because in the cathode sputtering process material is removed from the cathode by the effect of the luminous discharge, and deposited on the substrate, it is possible in the state of the art to remove material from the substrates by reversing the polarity, i.e., to etch the substrates. Such an etching process is suitable especially for the production of integrated circuits in which a pattern can be produced on the substrate by known techniques, the application of masks and appropriate photoresist varnishes.
Inasmuch as the substrate and its holder become the cathode in this known reversal of polarity, a good etching action is achieved, but as far as the apparatus is concerned, it becomes very complex, namely when substrates are to be alternately coated and etched in a continuous succession of operations. This would entail a constant change of the polarity of the substrates, which runs into considerable difficulty on account of the systems used for transporting the substrates. In substrates which are arranged, for example, on a round table and then carried through different work stations within the same or different vacuum chambers, such alternation of polarity would be extremely complicated.
Lastly, an apparatus for etching substrates by a luminous discharge in a vacuum is known (DE No. 22 41 229), containing a vacuum chamber, a substrate holder, an electrode, and a radiofrequency generator with an output frequency above 100 kHz, whose output electrodes are connected on the one hand to the substrate holder and on the other hand to the electrode. This known apparatus, however, also has the disadvantage that, in the etching of silicon wafers, a no more than satisfactory uniformity of the etching can be achieved.